On Monday, UN under-secretary for peacekeeping Jean-Marie Guéhenno raised the terrifying prospect that the UN-authorised peacekeeping force for Darfur may well have to be aborted because of obstructionism on the part of the Khartoum regime. Guéhenno declared that because of Khartoum's actions we are fast approaching a moment in which members of the UN security council will have to ask a critical question:

Do we move ahead with the deployment of a force that will not make a difference, that will not have the capability to defend itself and that carries the risk of humiliation of the security council and the United Nations and tragic failure for the people of Darfur?

The question, of course, answers itself. Privately, Guéhenno and other UN officials suggest an even gloomier picture of a mission that has already largely collapsed and is far behind on deployment benchmarks.

To be sure, the unprecedented UN/African Union "hybrid" mission in Darfur (UNAMID) has been badly compromised by the refusal of militarily capable nations of the world to provide the two dozen transport and tactical helicopters required, at a bare minimum, for security and protection operations in Darfur. Not a single Nato country has offered even one helicopter. Sadly, this serves as too accurate a measure of the real concern for Darfur on the part of those whose rhetoric has been most fulsome. But it is brazen obduracy on the part of the Khartoum regime that has created the deepest threat that the people of Darfur will be left entirely without protection, and that humanitarian operations will have to be suspended throughout the region. The UN estimates that 4.2 million people are currently in need of humanitarian assistance.

Of course Khartoum's obduracy has long been in evidence. Four months after the security council authorised the present peace support operation to Darfur under Resolution 1769, and 15 months after a previous security council resolution authorised a similar operation, Khartoum is still objecting to the UN/AU-proposed roster of countries that are to provide troops, civilian police and engineering and medical units. Khartoum refuses to grant landing rights to heavy transport aircraft or allow night flights (critical for both civilian protection and medivac needs). It refuses to grant adequate access to the Port of Sudan or expedited off-loading of equipment there. And it refuses to grant adequate land or water rights in the arid Darfur region.

What will follow from a UN decision to abort UNAMID? Utter catastrophe. The exceedingly weak, under-manned, and under-resourced African Union mission in Darfur will collapse entirely. This badly demoralised force is barely functioning now and is simply trying to hold on until December 31 2007, when the AU mission is supposed to be incorporated into UNAMID under UN auspices. But given Khartoum's obstructionism, this transfer will be at best symbolic: there may be UN auspices but no meaningful deployment of UN troops or resources. And as soon as it becomes clear that a meaningful UNAMID is not deploying, African nations will quickly withdraw their troops, which have already endured an unconscionable number of casualties, most at the hands of rebel groups that resent AU impotence on the ground and political accommodation of Khartoum's génocidaires by AU leaders. This will leave no protection forces of any kind, for civilians or humanitarians

Last January humanitarian organisations made clear they felt they had reached the furthest extreme of tolerable insecurity. One open letter came from a group of six distinguished nongovernmental organisations; another open letter came from all 14 UN operational humanitarian organisations in Darfur, including Unicef and the World Food Programme. No UN humanitarian operation had previously issued such a clear and public warning of impending collapse. These organisations, too, have been holding on with the hope that the UN would finally provide protection for them and the civilians they so courageously serve. If they are disappointed in their hopes, they will leave; an already intolerable situation will rapidly collapse into anarchy.

With no international presence - by the UN, by the AU or by international aid organisations - there will be nothing to constrain Khartoum or the rebels or the various armed elements and bandits that contribute so much to present insecurity. Confrontations between Khartoum's armed forces, including its Janjaweed militia allies, and camps for displaced persons are likely to escalate quickly, and may become a series of pitched battles. Khartoum is likely to use its Antonov bombers and helicopter gun ships in such battles, ensuring massively disproportionate civilian casualties in and around some 200 camps.

It is intolerable that the international community seems prepared to accept what will be cataclysmic human destruction. There can hardly be any doubt that the UNAMID force is badly conceived, has an ambiguous command-and-control structure, and is excessively reliant on African nations that cannot provide adequate numbers of fully-equipped, self-sufficient troops and civilian police per UN standards. The hybrid nature of the mission was itself a poorly calculated concession to Khartoum in the wake of the regime's defiance of the previous UN resolution authorising force to Darfur, Resolution 1706, passed on August 31 2006.

But UNAMID is now the only arrow in the quiver: there is no other force on the horizon, no other means for protecting civilians and humanitarians. If Nato nations aren't prepared to provide the 24 helicopters the UN mission requires, they are hardly likely to participate in or provide resources for any non-consensual deployment of force to Darfur, a nightmarishly difficult logistical and military undertaking in any event.

UNAMID must succeed. If it does not, the only question is only how long it will be before Darfur slides into cataclysmic destruction, with no means of halting that slide. This is the stark choice before the international community: is it prepared to see UNAMID fail, or will it rally the resources and exert the pressure on Khartoum, both of which are both critical to UNAMID's success?

The UN secretary-general and under-secretary for peacekeeping should send public, individual letters to every militarily capable nation within the world body, asking why it cannot provide at least one of the required helicopters. The public should make explicit demands of their governments, especially countries that possess significant amounts of military equipment, like the required helicopters: the US, the UK, France, Germany, the Netherlands, South Africa and India.

But again, the larger problem, and thus the larger task, is to exert sufficient pressure on Khartoum to end its obstructionist ways. The key here is China, widely recognised - including within the UN's political offices - as having unrivalled leverage with the National Islamic Front (National Congress Party) regime. China alone of the major powers can demand of Khartoum (if no doubt behind closed doors) that the broad campaign to stall and ultimately eviscerate UNAMID must end. And yet, a well-placed UN official recently told me that it is the consensus at Turtle Bay that China was becoming more, not less, supportive of Khartoum's intransigence. After a brief but apparently successful Darfur public relations campaign, Beijing has evidently decided that it may resume its uncritical support of all decisions made by the NIF regime, no matter what the consequences for the people of Darfur.

Either this changes, or there is no chance that Khartoum will be moved by other actors. In turn, this obliges nations like Germany, France, the US, and the UK to use the very considerable leverage deriving from their individual bilateral relations with Beijing to push China to act. Currently, all four of these major Western powers have moved Darfur to the third- or even fourth-tier in bilateral relations. Germany and France seem much more concerned about trade relations with China than Darfur, despite the tough talk coming from Angela Merkel and Nicolas Sarkozy. The UK under Gordon Brown seems adrift after years of vacuous rhetoric from Tony Blair's government. And the US places Taiwan, North Korea, Iran, trade and international terrorism far, far above any professed concern for Darfur. Again, civil society must play the key role of demanding that China, vulnerably exposed host of the 2008 Olympic Games, be pushed hard to use its massive influence with Khartoum to change the regime's behaviour.

It's a long shot. But the odds against protecting the people of Darfur become greater every day, and we are now at the tipping point. Urgency is the essential watchword: we have only days or weeks before allowing events to be set in motion that will see many hundreds of thousands of people die.